Constant current constant voltage regulator



Dec. 3, 1968 w, GLASGOW ET AL 3,414,803

CONSTANT CURRENT CONSTANT VOLTAGE REGULATOR Filed Aug. 24, 1966RECTIFIER FILTER E 0 W 3 2 A v a TL R E0 4 f mm /5 .w .m R E .l v L eAis w w n u! a a w. TEW EEMI s NCT GCTI R EN AN f. E TA am? a? JI J|CBMVBM IL 6 7 8 a a e m p u; .CHT 4" E3 n F100 .W "M M9 g y H SERIESCONTROL ELEMENT s a a M 4 W A: 0 i V u l 2 r R R E .T 5 k. E

R v/ E w U w a A R TER 6 EE GCW NCW s m w Ema R s LL L r N w n wmmc I MBD 0 If m E 5 .L 4 B .m W a T m m E s 8 Hm FT 3 Tm RF R United StatesPatent Oflice Patented Dec. 3, 1968 3,414,803 CONSTANT CURRENT CONSTANTVOLTAGE REGULATOR Paul W. Glasgow, Oakhurst, Robert A. La Falce,Neptune, and John D. Baugher, Little Silver, N.J., assignors to TheRowan Controller Company, Westminster, Md., a corporation of MarylandFiled Aug. 24, 1966, Ser. No. 574,783 6 Claims. (Cl. 3234) ABSTRACT OFTHE DISCLOSURE A regulator having a series control transistor and acurrent sensing resistor to provide constant voltage or current. Aconstant current mode of operation is provided utilizing the currentsensing resistor when the output voltage is below a preselected value. Abridge circuit provides a constant voltage mode of operation when theoutput voltage attains the preselected value. A pair of transistorsswitch the regulator from one mode to the other. A buffer circuit,connected across the sensing resistor, eliminates the error produced bycurrent required for constant voltage regulation while operating in theconstant current mode.

This invention relates to a power supply and more particularly theinvention relates to a power supply which is capable of delivering tooutput terminals a constant current of selected magnitude oralternatively a constant voltage of selected magnitude, the regulatorincluding means for automatically switching from one operating mode tothe other.

In constant current regulators, it is common to use a sensing resistorwhich is variable to select the current to be delivered to the load. Thevoltage drop across the sensing resistor is detected and utilized tocontrol or hold the current in the load constant. In a constant voltageregulator, the voltage at the output terminals is detected and isutilized to hold the voltage at the output terminals constant. Anobjective of the present invention has been to provide a power supplyhaving an unregulated voltage source, control means and distinct currentand voltage regulating systems for actuating the control means so as todeliver to a single output constant current or constant voltagedepending on the mode of operation.

When operating in the constant current mode, the voltage regulator isheld inoperative by the switching means referred to above butnevertheless there is a finite current which flows into its sensingpoint. If its sensing point is between sensing resistor and the outputterminals, then the regulator, in the constant current mode, would beinaccurate by the amount of current which does not flow to the outputterminals, but rather circulates into the voltage regulator. Where theconstant current supplied to the output terminals is large, that is,several amperes, the error produced bythe circulating current isinsignificant, for the operation of the voltage regulator requires but afew milliamps. However, where the power supply is required to supplycurrents of the order of a few microamps, then a circulating current inthe voltage regulator of several microamps would produce an intolerableerror.

If the sensing point for the voltage regulator is between theunregulated power supply and the current sensing resistor, no errorwould be introduced in the current regulator, but the voltage regulatorwould be inaccurate by the amount of the voltage drop across the sensingresistor.

In accordance with the present invention, the voltage regulator isconnected to the circuit at a point between the unregulated power supplyand the sensing resistor and a buffer circuit is connected between thesensing point and the input to the voltage regulator, the buffer circuitsimulating the voltage drop across the sensing resistor. Thus, while thepoint of connection is on the power supply side of the sensing resistor,the effective potential applied to the voltage regulator is at thepotential of the output terminal.

It has been another objective of the invention to provide a currentregulator for supplying current of the order of microamps to the outputterminals. Such a lower order constant current regulator of itselfpresents problems for some current must flow in the current regulatingnetwork across the sensing resistor. In order to keep this as low aspossible, the invention provides a balanced detector having a highenough input impedance that the current input to it is in the low nanoamp (10- range, the detector provides a current gain sufficient to drivethe amplifiers necessary to operate the system.

It has been another objective of the invention to provide a specialswitching network at the output of the current regulator network andvoltage regulator network for selectively determining the mode ofoperation of the power supply. Through the use of the switch of thepresent invention and associated power supply circuitry, it is possibleto set the power supply for a specific current and a specific voltageand operate the first on the constant current mode until the loadresistance is increased to the extent that the preselected voltage atthe output terminals is attained whereupon the operation automaticallyand insantaneously shifts to a constant voltage mode.

These and other objectives of the invention will become more readilyapparent from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a circuit diagram of a power supply in accordance with thepresent invention,

FIG. 2 is a bridge circuit illustrating the operation of the DeBlasiovoltage regulator utilized in the power p y,

FIG. 3 is a circuit diagram of the balanced current detector utilized inthe power supply, and

FIG. 4 is a circuit diagram of an alternative manner of connecting thevoltage regulator.

Referring to FIG. 1, the voltage regulator includes an alternatingcurrent source 10 coupled through a transformer 11 to a rectifier andfilter system 12 to provide an unregulated direct current voltage Eacross a positive line 13 and a negative line 14.

The positive line includes, in series, a series control element 16 whichis an NPN transistor having a collector 17 connected to the unregulatedoutput E and emitter 18 connected to the output side of the regulatorand a base 19 to which control signals are applied. It should beunderstood that the control element 16 could be a PNP transistorinserted in the negative line 14 and the additional circuit elementswould be in a mirror image relation to the circuit, as described below.

The regulator has a positive output terminal 20 and a negative outputterminal 21 across which an output voltage E is produced. The regulatormay be provided with voltage sensing terminals as is common in this art.

The series control element 16 regulates the output voltage or currentthrough the load attached to the output terminals by varying theconductance or inversely the resistive effect of the series controlelement. When the positive voltage on the base 19 is high, the resistiveeffect is low and, conversely, when the voltage on the base is low, theresistive effect is high.

The signal applied to the base 19 is derived either from a currentregulator system or from a voltage regulator system, the system incontrol being determined by a switch 25.

The current regulator includes a sensing resistor R which is connectedin series with the positive line 13. The sensing resistor is variableand preferably is constituted by decaded resistors having suitableswitches to control the net resistance of the sensing resistor and maybe of the type described in copending application Ser. No. 532,633,filed Mar. 8, 1966.

A current reference voltage E, is connected at its positive terminal 26to the high side of sensing resistor R and at its negative terminal 27to one side of a current balanced detector 28. The low side of thesensing resistor R is connected through line 29 to the other side of thecurrent balanced detector 28. The terms high and low refer to the highpotential and low potential sides of the sensing resistor, assuming theconventional flow of current from plus to minus.

The current balanced detector which detects a difference in potentialbetween lines 27 and 29, amplifies it, and feeds an output signal to theoutput 30 of the detector. The preferred circuit for the detector willbe described below and is shown in FIG. 3.

The output 30 is amplified by an amplifier and is connected to a PNPtransistor 31 at its base 32. The transistor 31 has an emitter 33connected in series with a resistor 34 which is connected to thepositive side E of a power supply. The transistor 31 has a collector 35connected to the negative side E of the power supply. The power supply E-E supplies both a positive and negative potential with return to thepositive line 13 at the low side of the series control element 16 sothat the power supply floats with variations in potential of thepositive line 13.

Current regulator operation When the regulator is in the currentregulator mode of operation, the balanced detector 28 compares thevoltage drop across the sensing resistor R to the reference voltage EWhile a current change might be due to any of a number of causes, let itbe assumed that the current has dropped by adding resistance across theoutput E The potential difference across sensing resistor R is reducedand the line 29 becomes positive with respect to the line 27. Thispotential difference is detected by the current balanced detector 28 andthe output of the balanced detector is such as to raise the potential onthe base 32 of transistor 31, thereby permitting less current to flowthrough the transistor 31. The reduction of current through thetransistor 32 raises the potential of the junction point 36 and henceraises the potential on the base 19 of the control element to permitgreater current to flow through the control element. This conditioncontinues until a balance is achieved between the potentials acrosslines 27 and 29.

Voltage regulator system The voltage regulator employs the basiccircuitry described in DeBlasio Patents Nos. Re. 24,800 and 3,138,- 752.The circuit includes a decaded variable resistance R, in series with aresistance R and forming a voltage divider therewith and a referencevoltage E having its negative terminal connected to the positive line 13through a positive sensing buffer 40. The junction between R and R isconnected by line 41 to one input side of a voltage balanced detector42, the other side being connected to a sensing point 43 which is commonto the negative side of the reference voltage E and the positive side ofthe output terminal. As will be explained below, the sensing bufferholds the point 43 at the output potential of positive terminal 20.

The voltage balanced detector 42 has an output line 45 connected to abase 46 of a PNP transistor 47. The transistor 47 has its emitter 48tied to the emitter 33 of transistor 31. The transistor 47 has acollector 49 connected to the negative side E of a power supply.

The voltage regulator of the invention uses the DeBlasio bridge circuitconfiguration. As more clearly illustrated in FIG. 2, one side of thebridge is constituted by the voltage 4 divider R R with thejunction'point 41 of the voltage divider being connected to the balanceddetector. The other side of the bridge is formed by the referencevoltage E in one leg and in the other leg, the unregulated source E andthe series control element 16.

In accordance with this DeBlasio regulator circuit of FIG. 2, the outputvoltage E is equal to the drop across variable resistor R and, as aconsequence, the output voltage can be determined by the selection ofthe value of the resistance R While the DeBlasio bridge is preferred,the present invention is not restricted to its use.

Positive sensing bufier As has been indicated above, the connection ofthe voltage sensing point 43 to the line of the regulator is of criticalimportance. If the connection is made at the output terminal, then,during operation of the invention on the current mode, current flowsinto the voltage balanced detector through the sensing point 43 as wellas into the load across the output terminal E Since the sensing resistorR is detecting the total current flowing to the output terminals, thebalance attained by the balanced detector is in error by the amount ofcurrent flowing into the voltage balanced detector 42. Where the desiredoutput current is small, that is, of the order of microamps, thepercentage of error introduced by current circulating into the voltagebalanced detector is large.

On the other hand, if the sensing point 43 is connected to the high sideof the sensing resistor R in order to avoid error in the currentregulator, a similar error is introduced in the voltage regulatorsystem. The sensing point 43 detects not the output voltage but ratherthe output voltage minus the drop across the resistor R These errors aresubstantially eliminated through the use of the buffer 40 which connectsthe sensing point 43 to the high side of the sensing resistor R Whilemaintaining its level of potential the same as that of output terminals20. Thus, by connecting the point to the high side of the sensingresistor, the accuracy of the current regulator is not impaired and byusing the buffer to maintain the potential of the sensing point 43 atthe level of the output terminal 20, the accuracy of the voltageregulator network is not impaired.

The buffer network includes a source voltage E and a transistor controlelement 50 connected in series with the input to detector 42. Theseelements are to produce a voltage drop equal to the drop across resistorR The control element 50 has an emitter 51 connected to one input 52 ofa balanced detector 53. The other input 54 to the balanced detector isconnected to the output terminal 20. The output 55 of the balanceddetector is connected to the base 56 of the transistor 50. The balanceddetector regulates the voltage on the base 56 so that the potential atthe point 52 which is common to the sensing point 43 is the same as thepotential of the output terminal 20. Thus, the buffer system 40 causesthe sensing point 43 to reproduce the potential at the output terminal20 without being connected directly to it.

Operation f the regulator In describing the operation of the regulator,it will be assumed that the regulating variables, principally R and Rare preset to provide a current regulating function while the outputvoltage remains below volts. However, R is set to provide constantvoltage regulation at 100 volts. Thus, when the resistance of the loadconnectedacross the output terminals 20 and 21 becomes so great that theoutput voltage rises to the level of 100 volts, the regulator willchange from a current regulating mode to a voltage regulating mode. Itwill be understood that voltage regulation can be achieved at lowervoltages simply by proper selection of the value of the R In the steadystate condition, the switching transistor 31 in the current regulatorcircuit is functioning and the switching transistor 47 in the voltageregulator is biased to cut off, that is, its base is at such a highvoltage level that its emitter-base junction is reverse biased.

As resistance is inserted in the output, the current tends todrop andthe current regulator calls for a correction,

that is, to raise the current to the original level. It does so byincreasing the potential on the base 32 of transistor *31. This causesless current to flow to the emitter '33 and raises the potential of thejunction point 36. This raises the potential on the base 19 of thecontrol element 16,

'driving it into further conduction so that increased cur- 'ren'tfiowstothe load, thereby maintaining the current constant.

As the resistance increases with a constant current through the load,the voltage across the load must necessarily increase. When it reachesthe 100 volts, the system is providing'the current for which the.regulator is programmed and the voltage for which the regulator isprogrammed.

As additional resistance is placed in the circuit, the current againtends to decrease at the crossover point. The current regulator callsfor more current and the voltage balanced detector comes intoequilibrium and starts to maintain constant voltage. In the currentregulator, the bias potential on base 32 of transistor 31 becomes morepositive, moving toward cutoff. In the voltage regulator, the base 46 oftransistor 47 becomes more negative, moving toward saturation.Effectively, the resistance of transistor 31 is increasing and theresistance of transistor 47 is decreasing.

Consequently, more current is drawn through resistor 34, dropping thepotential at point 36. As the potential of point 36 drops, the potentialon the base 19 of transistor 16 drops, thereby permitting less currentto flow to the output and hence the output voltage remains constant at100 volts.

Current balanced detector The current balanced detector 28 isdiagrammatically illustrated in greater detail in FIG. 3. The inputconnections 27 and 29 are applied to the bases of transistors havingvery high input impedance. The transistor must also have a very low ICBOcharacteristic, that is, the collector to base current (leakage current)must be very low. The specific transistors employed are 2N930Atransistors although any transistors having com-parable or even superiorcharacteristics may be employed. The transistors are connected as abalanced Darlington amplifier, the input stage drawing at its base about4 nano amps.

The balanced detector is preferably connected to provide two outputstages at 60 and 61 and the output from each of these stages is fed intotwo inputs of a balanced amplifier 62. Through the use of this system,it is possible to double the voltage gain in the whole system.

Alternative forms of the invention While the sensing buffer of thepresent invention has been shown and described in the specific circuitof FIG. 1, it should be understood that modifications can be made toprovide circuits which utilize the sensing buffer concept but which donot depart from the scope of the present invention. For example, thecontrol of both the current and voltage is effected by a transistorcontrol element 16 connected in series with one of the output lines ofthe power supply. In practice, more than one such transistor areutilized and connected in parallel in order to handle the powerrequirements of the system. Further, the regulator system, particularlyincluding the sensing buffer, can be used with control means other thana series connected transistor. For example, the control means employedcan be an SCR circuit as is known in the regulator art.

The preferred circuit does not necessarily require the control elementand sensing buffer to be in the positive line of the power supply. Amirror image of the illustrated circuit will work equally as well withthe principal elements being in the negative line of the power supplyand with corresponding changes made in the polarity and orientation ofthe reference voltage, the transistors, and the like.

The circuit will work equally as well when the series control element 16and the sensing resistor R are in opposite output lines as shown, forexample, in FIG. 4.

The circuit of FIG. 4 is substantially identical to the circuit of FIG.1 except that the sensing resistor R has been placed in series with thenegative line and the sensing buffer for the voltage regulator has beenconnected to the negative side of the power supply. The functioning ofthe circuit is otherwise identical to that described in connection withthe circuit of FIG. 1.

We claim: 1. A combined current and voltage regulator comprisanunregulated power supply having positive and negative output linesterminating in output terminals, output control means associated withsaid power supply for varying the current and voltage at said outputterminals, a resistance in one of said lines, current regulating meansconnected across said resistance and including a reference voltage, saidcurrent regulating means comparing the voltage drop across saidresistance to said reference voltage, said current regulating meanshaving an output connected to said output control means for varying thecurrent to bring the reference voltage and voltage drop into balance,

voltage regulating means having input leads connected across said outputlines and including a reference voltage source, said voltage regulatingmeans comparing the output voltage to said reference voltage and havingan output connected to said output control means for varying itsresistance to bring the output voltage and reference voltage intobalance,

one input lead to said voltage regulating means including a buffercircuit, said buffer circuit being connected to a detecting pointbetween said resistance and output control means,

said buffer circuit including means for detecting the voltage dropacross said resistance and applying an equivalent voltage drop in saidinput lead.

2. A regulator according to claim 1 in which said buffer circuitcomprises a sensing voltage source and a variable resistance controlelement connected in series with said input lead,

a balanced detector connected across the output terminal and the inputto said voltage regulator means, said balanced detector having an outputconnected to said control element.

3. A regulator according to claim 1 in which said buffer circuitcomprises,

a series control circuit including a voltage source and a transistorhaving a base and having a collector and an emitter connected in serieswith said voltage source,

said control circuit being connected between said detecting point andthe input to said voltage regulating means,

a balanced detector connected across the input to said voltageregulating means and the side of said resistance opposite said detectingpoint, said balanced detector having an output connected to the base ofsaid transistor.

4 A regulator according to claim 1, further compl'lSlng,

switch means connected between said output control means and saidcurrent and voltage regulating means,

said switch means rendering said voltage regulator inoperative until theoutput voltage reaches a preselected level, and renders said currentregulator inoperative when said output voltage reaches said preselectedlevel.

5. A regulator according to claim 4 in which said switch means comprisesa pair of transistors each having a base, and emitter and a collector,

said transistors having one of their remaining like terminals connectedtogether at a junction point and the oher of their like terminalsconnected to reference voltages, the outputs of said current andvolttage regulators being connected to respective bases of saidtransistors,

said junction point being connected through a resistance to a voltagesource of opposite polarity to said reference voltage,

said junction point being connected to said output control means.

6. A combined current and voltage regulator comprising,

an unregulated power supply having positive and negative output linesterminating in output terminals,

a variable resistance control element in one of said lines,

a resistance in one of said lines,

current regulating means connected across said resistance and includinga reference voltage, said current regulating means comparing the voltagedrop across said resistance to said reference voltage, said currentregulating means having an output connected to said control element forvarying its resistance to bring the reference voltage and voltage dropinto balance, voltageregulating means .having input leads connectedacross said output lines and including a reference voltage source, saidvoltage regulating means come parin the output voltage to said referencevoltage and having an output connected to saidjcontrol element for,varying its resistance to bring the output voltage and referencevoltage, into balance, one input lead to said voltage regulating meansinclud ing a buffer circuit, said butter circuit being con"- nected toat detecting point between said resistance and said control element, A lf i said buflFer circuit including means for detecting the voltage dropacross said resistance and applying an equivalent voltage drop in saidinput lead.

References Cited V p UNITED STATES PATENTS LEE T. HIX, Primary Examiner.a A. D. PELLINEN, Assistant Examiner.

